In the past, many suspension control apparatus of this type have been known, some examples of which are disclosed in Japanese Utility Model Laid-Open No. 61-163710 or Japanese Patent Laid-Open No. 62-34808. In these conventional suspension control apparatus, a fuild spring chamber such as a pneumatic spring chamber is interposed between each road wheel and the body of a vehicle so that supply to and discharge from the fluid spring chamber of compressed air is controlled in an appropriate manner to suppress rolling of the vehicle body. Specifically, there is a tendency that when a vehicle is steered to turn, the suspension units disposed on the turning side of the vehicle are forced to contract under the action of centrifugal force whereas those on the opposite side thereof expand. In order to suppress this tendency, a predetermined amount of compressed air is supplied to the fluid spring chamber of each of the suspension units on the contracted side, and at the same time a predetermined amount of presure air is discharged from the fluid spring chamber of each of the suspension units on the expanded side so as to incline the vehicle body in the opposite direction, thereby maintaining the attitude of the vehicle body in a horizontal manner.
Many control apparatus for vehicular suspension systems other than the above have also been studied and proposed which are intended to provide the same effects as described above by appropriately changing the damping force or spring constant of each suspension unit, or by regulating the operations of stabilizers.
With the above described conventional control apparatus for vehicular suspension systems, in cases where a transverse acceleration (i.e., an acceleration in a direction perpendicular to the longitudinal direction) of a vehicle is detected by an acceleration sensor so as to calculate the magnitude of rolling of the vehicle for control of the supply and discharge of compressed air or other suspension characteristics, it is required to precisely determine a neutral point on the basis of which the detection of vehicle acceleration in a transverse direction is effected. In the past, however, no correction or compensation has been made for such a neutral point with respect to the output of an acceleration sensor which is liable to change as time passes. As a consequence, there arises a problem that it is difficult to carry out roll-suppression control with a high level of preciseness over an extended period of time. Thus, it has been long desired to effect a correction or compensation of such a neutral point in an automatic fashion.